Britain cannot afford its defence plans on the present budget, the House of Commons defence committee reports today - and this can hardly be news to a regular reader of Comment is Free. The defence committee says that at least one major programme needs to be cut, because the process of shaving funding off numerous programmes - known in the trade as "salami slicing" - has reached its limit.

But beneath the report on defence equipment procurement lies a much bigger question: who exactly is running defence and security policy in this country, and on what criteria. The obvious answer is Gordon Brown - who has been running defence through the Treasury since New Labour came in nearly 11 years ago.

Brown's political camouflage, that it was really Tony Blair who drove defence policies and pushed Britain into adventures in Kosovo, Sierra Leone, Macedonia, Afghanistan and Iraq, has now worn thin. Brown assented in cabinet to all these escapades and through the way he released or withheld funds he was hugely influential in their running.

His dabs are all over the latest episode of churning and burning in the defence world, be it over the future of the war operations in Iraq and Afghanistan or the way the men and women of the services are funded, paid, equipped and supported. And the criteria by which the man in No 10 and his acolytes at the Treasury operate aren't entirely based on the prime needs of the defence and security of Britain and its allies.

With a defence budget of around £34bn a year, the UK cannot afford the present range of operations abroad and the ambitious equipment-buying programme on which the defence ministry is currently embarked. The defence committee says today that at least one major programme should be cut altogether.

The obvious candidate is the plan announced last year to build two 65,000 tonne aircraft carriers - our biggest ships ever - at a cost of around £4bn. The programme is likely to cost between three and four times that sum once the aircraft are purchased and the combat systems are in place.

The service chiefs reluctantly decided to reconsider the carrier programme. The carriers' main task was to support land operations and, while desirable, they are not vital. However, the service chiefs have been told that the carriers are deemed to be "politically essential" by the present prime minister and cabinet.

This is because the programme will ensure that two shipyards on the Clyde will be kept open as will the facility at Rosyth, adjacent to the Dundee constituency of Gordon Brown and that of the defence secretary Des Browne on the other side of the Firth of Forth.

The carriers threaten to become the Frankenstein's monster of defence procurement. The navy are hooked on the programme. They have run down the fleet of surface ships, destroyers and frigates in the hope that they get the highly prestigious carrier programme. However, there is now a real risk that the aircraft carriers could become the ultimate defence oxymoron - carriers without any aircraft. The carriers are always built round the aircraft, rather than the other way round.

The new carriers are designed for the Lockheed Martin F-35 joint strike fighter. With the costings now running between a quarter and a third of a trillion dollars this is the most costly combat aircraft programme in history. "We might just be able to afford the ships, but on the present numbers we couldn't afford the planes," a senior British officer told me last week.

However, Gordon Brown, Des Browne and Alistair Darling might be surprised at just how radical the defence chiefs, and some of the MoD consiglieri, are prepared to be to make the current budget work. Today they are to announce the biggest PFI ever undertaken by the MoD, the £13bn package to lease up to 20 tanker-freighter aircraft based on the Airbus A330. These planes will fly for at least 30 years; can be used as freighters and surveillance platforms. They could also carry stand-off munitions, missiles and bombs.

The planes will replace ageing VC10s, some nearly 40 years old, and creaking Tristars. The plan to get them has been pushed through against tough opposition from the Treasury, because of its general dislike of PFIs as a concept.

The army, too, has decided to carry out its own internal radical review of its role, requirement and capability in terms of what Britain needs for defence, security, and humanitarian operations over the next few decades. They may show they can do radical better than the kitchen cabinets in Nos 10 and 11 Downing Street.

The problem with the defence budget, as I have written for years now, is that it is designed for a nation at peace, not one that is fighting in two serious regional wars. The other major ministries have complained against the MoD's questioning of the settlement for its budget under Gordon Brown's comprehensive spending review settlement of 2007. The other ministries are not prepared, apparently, to countenance that the MoD has to cope with the unpredictability of budgeting for two small wars.

"The problem is that the Labour party and government don't seem to have much of an idea of the real cost of defence, as a major policy item, in today's world," said a former defence chief to me recently. "As for the other side, the Conservatives, they just don't have a clue."